The present invention relates to a circuit generating high voltage and, more particularly, to a circuit including a voltage stabilizer proximate to an output coil of a fly-back transformer so as to stabilize the voltage on the output-coil side, wherein a diode is electrically connected to one terminal of the output coil on its low voltage side, and the ground potential at the anode side of the diode is controlled by the device for stabilizing voltage disposed on the low voltage side so that output potential for DC high voltage may be kept at a constant thereby attaining satisfactory stabilization of the output.
In the conventional circuit generating high voltage of the preferred form, there is known an typical circuit wherein, for the purpose of stabilizing a output potential for DC high voltage thereof, a device for stabilizing high voltage is electrically connected to the high voltage side of an output coil and controll for voltage stabilization is performed on the high voltage side. FIG. 1 shows a circuit drawing of such example proposed previously by the present inventor, wherein there are included a fly-back transformer 1 and a device 2 for stabilizing voltage.
The fly-back transformer 1 has an input coil 11 and an output coil 12. The input coil 11 is normally and electrically connected to a switching element such as a transistor and the others, and a DC input is turned on and off by the switching response of such element, so that the input coil 11 is driven by pulses derived from the above process. The output coil 12 is divided plurally into the number of "n" sections, and sectional coils from 121 to 12n are connected in series to one another via diodes from 31 to 3n respectively. The direction of diodes from 31 to 3n are so determined as to position in forward direction to the fly-back voltage generated in each coil of individual section from 121 to 12n, thereby comprising a device for rectifying a fly-back voltage rectifier. The fly-back transformer 1 further has the coil 13 for control and the coil 14 for an auxiliary power supply to be used for the device 2 for stabilizing voltage. 4 illustrates a capacitor to form a smoothing circuit.
The device 2 for stabilizing voltage is electrically connected to the control coil 13 disposed in the fly-back transformer 1 so as to control for the voltage stabilization on the high voltage side. The device 2 for stabilizing voltage comprises the device 21 for detecting voltage, the power supply 22 of a base voltage, the control circuit 23 and the others. The device 21 for detecting voltage yields a required signal for detecting voltage from a voltage signal obtained by dividing in accordance with resistances R1 and R2 the output voltage Vo for DC high voltage generated at an output terminal 5, and also from a base voltage obtained from the power supply 22 for base voltage. Such device 21 for detecting voltage can be composed of a error amplifier, a comparator, and the otheres.
The control circuit 23 is supplied with the signal for detecting voltage from the device 21 for detecting voltage. This circuit 23 is electrically connected between the output terminal of a rectifying-smoothing circuit composed of a diode 6 and a capacitor 7 connected to the control coil 13, and the rectified output terminal of the sectional coil 12n positioned in the highest voltage stage of the output coil 12. One terminal of the control coil 13 is connected to the rectified output terminal of the sectional coil 12n via the diode 8.
The device 2 for stabilizing voltage is supplied with a dynamic electric power from the rectifying-smoothing circuit 9 electrically connected to the coil 14, for auxiliary power supply.
When there occurs any deviation in the output voltage Vo for DC high voltage, the voltage signal divided in accordance with resistances R1/R2 and inputted to the device 21 for detecting voltage is changed in accordance with such deviation. The device 21 for detecting voltage then functions to compare the voltage signal with the base voltage yielded from the power supply 22 for base voltage or amplifies the difference between the said two voltages and feeds to the control circuit 23 a signal for detecting voltage which is proportional to the deviation. And in response to the signal for detecting voltage fed from the device 21 for detecting voltage, the control circuit 23 controls the voltage added from the coil 13 for control to the high-voltage output terminal of the output coil 12, thereby eliminating the deviation of the output voltage Vo for DC high voltage to consequently keep the said output voltage constant.
However, in the circuit for stabilizing output mentioned above, the device 2 for stabilizing voltage is electrically connected to the high voltage side of the output coil 12, so that the ground potential of the device 2 for stabilizing voltage is rendered extremely high to eventually bring about considerable difficulties in the process for ensuring insulation. Furthermore, there exists the necessity of additionally providing the coil 13 for control to complicate the circuit configuration as a result. Besides the above, in the circuit generating high voltage mentioned above, the capacitor 4 for smoothing is electrically connected between the output terminal of the rectifying device and the ground, and the device 2 for stabilizing voltage is included within the loop of circuit comprising the output sectional coils from 121 to 12n, the device from 31 to 3n for rectifying and the capacitor 4 for smoothing. Therefore the voltage stabilizer 2 is harmfully affected by the voltage pulsation caused in the said loop of circuit to consequently increase the overshoot and the undershoot of the output potential Vo for DC high voltage while bring about another problem of prolonging the recovery time. Now an exemplary case will be described below with regard to a unit generating high voltage which produces the output voltage of 29 KV for DC high voltage. FIG. 2 shows a waveform drawing of dynamic signals in individual portions of a unit generating high voltage designed to yield a output voltage of 29 KV for DC high voltage, wherein Io represents the waveform of the output current flowed out from an output terminal 5, and Vo represents the waveform of the DC high voltage.
In the above-described circuit, as is apparent from these waveform drawings, the value deviated by high voltage resulting from the overshoot and the undershoot reaches 35 Vpp or so, and the recovery time of such overshoot and undershoot becomes longer than 2.5 msec., whereby the current is changed prior to restoration of the high voltage to the initial state. FIG. 2 shows that even after the lapse of more than 5 msec. which corresponds to the time of one cycle, the voltage is not yet responsive to the current change.